Metal Detector
a metal detector and detector technology, applied in the field of metal detectors, can solve the problems of high cost of electronic components and relatively high electromagnetic interference risk of time domain detectors, and achieve the effect of low cost and low cos
Active Publication Date: 2008-04-24
MINELAB ELECTRONICS
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Benefits of technology
[0011] An object of this invention is therefore to provide a metal detector improvement at relatively low cost that assists an operator such as a prospector in the location of targets.
[0012] The current invention alleviates at least some of the problems of the prior art by applying a switched voltage signal to a magnetic transmitter and a receiver including approximate sine-wave weighted synchronous demodulation which receives a magnetic field synchronously with the switched voltage signal. An operator may select the frequency profile of the approximate sine-wave weighted synchronously demodulation, the transmit switched output voltage signal may also be appropriately altered when the user selects different approximately sine-wave weighted synchronously demodulation profiles, which may include frequency change and number of relatively strong frequencies transmitted. The electronics may be low in cost by the employment of digital signal processing and switching circuitry.
Problems solved by technology
The electronics in such detectors is often expensive.
Time domain detectors are relatively highly susceptible to electromagnetic interference owing to wide receive bandwidths.
Method used
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[0026]FIG. 1 shows a switched voltage signal generated by switching electronics 2 is applied to a magnetic transmitter 1, shown here as a transmit coil. Signals from a magnetic receiver 3 are amplified by a preamplifier 4 and applied to applied to approximate sine wave weighted synchronous demodulators 5. The output of these demodulators is fed to further signal processors 6 which provide a useful output signal, such as an audio alert or visual display. Both the transmitter and synchronous demodulators are controlled by a controller 7 which includes a clock to control timing. An operator selects the frequency profile of the approximate sine-wave weighted synchronously demodulation by operating switches 8, which may also alter the switched voltage signal appropriately too.
[0027]FIG. 2 shows a switched voltage signal of fundamental period T, whose waveform repeats, and this is relatively rich in frequencies 1 / T, 4 / T and 16 / T. This waveform and the corresponding receive sine-wave demo...
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A real time electronic metal detector including a magnetic transmitter (1) and a receiver (3), wherein the receiver includes approximate sine-wave weighted synchronous demodulation and a switched voltage signal is applied to the magnetic transmitter and the said receiver approximate sine-wave weighted synchronous demodulation is selected to receive synchronously with the switched voltage signal, such that the switched voltage signal and the receiver approximate sine-wave weighted synchronous demodulation may be altered by means of operator selection.
Description
TECHNICAL FIELD [0001] The current invention relates to a metal detector and has particular application to coin, treasure, prospecting and landmine detectors. BACKGROUND ART [0002] Some commercially available analogue electronics based single frequency sinusoidal signal transmitting metal detectors have switches which allow a user to select different frequencies. The electronics in such detectors is often expensive. The ability to select different frequencies may be useful, for example, in gold nugget prospecting where the size of gold nuggets may vary from location to location and hence the optimal frequency for detection may also vary. [0003] U.S. Pat. No. 5,537,041 discloses a metal detector which transmits multi-period pulses and operates in the time domain, as too do most, and probably all, commercially available pulse induction metal detectors; for example those disclosed in U.S. Pat. No. 4,868,504 and U.S. Pat. No. 5,576,624. Time domain detectors are relatively highly suscep...
Claims
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IPC IPC(8): G01V3/10
CPCG01V3/104
Inventor CANDY, BRUCE HALCRO
Owner MINELAB ELECTRONICS